One proposed structure of a power output apparatus includes an engine, a planetary gear unit including a carrier and a ring gear respectively connected with a crankshaft of the engine and with a driveshaft mechanically linked to an axle of a vehicle, a first motor arranged to input and output power from and to a sun gear of the planetary gear unit, a second motor arranged to input and output power from and to the driveshaft, and a battery designed to transmit electric power to and from the first motor and the second motor (see, for example, Japanese Patent Laid-Open Gazette No. 2005-39880). This proposed power output apparatus inputs and outputs a power from and to the driveshaft via the ring gear based on the power input from the engine to the carrier and the power input from the first motor to the sun gear, while controlling the second motor to input and output a power from and to the driveshaft.